The present invention relates to a backlighting apparatus for displays, particularly for small-area liquid-crystal displays (LCDs), such as utilized in virtual reality headsets. LCDs, which allow the display of alphanumeric, graphic or other information, may comprise a medium whose transmittance changes in response to the application of an electrical potential across the medium. The LCDs may be viewed even in an otherwise dark environment by applying illumination uniformly to their rear face. An exemplary backlighting apparatus for an LCD is disclosed in U.S. Pat. No. 4,043,636.
It is desirable for a backlight for small-area LCDs, such as those found in helmets of virtual reality systems, to have certain attributes. Firstly, it must have an acceptable level of brightness. Secondly, it is preferable to have a spectral distribution that is as white as possible, particularly if the LCDs display color images. The light source must be compact, and preferably require little maintenance. Lastly and most importantly, the lighting system must provide uniform illumination across the entire area of the display. This latter need translates into a requirement that the light emerging from the light source be featureless and free of distortions such as holes or rings. In practice, the requirement of uniform illumination is difficult to achieve, and prior art devices frequently fail to provide a sufficiently uniform source of illumination for LCD displays. Additionally, prior art devices frequently relied on light guides to direct light to reflective surfaces, necessitating complicated geometries and added weight and expense.
An object of the present invention is therefore to provide a simple, compact, lightweight means for backlighting a display, typically a small-area LCD display, which provides highly uniform, high-intensity illumination of the entire display panel.